Red is the colour

Sadly, my paper about redness was not selected for publication.

Nevertheless, I enjoyed writing it and learned a great deal. For example, I did not know that birds cannot produce redness without eating plants or insects (who've eaten the plants) that contain carotenoids. These chemicals - which are also useful in other biological functions (immunity, for example) - have to be metabolised to make the colours orange and yellow. Further processes are required to make red. So "being red" is expensive. Those birds growing up in a place where there are not sufficient carotenoids around, or who cannot afford to use them all for plumage, may look washed out.

Apparently, research shows that urban kestrels have a lower level of carotenoids in their plasma, due to the diet available in urban areas. Now that red kites are returning to city skies, I wonder if they will start to become less red?

Now, what about the redness, or orangeness, of autumn leaves? We know that trees reabsorb useful chemicals from the leaves, so that the "hidden" colours of carotenoids and other chemicals are revealed. I thought they also put chemical waste into the leaves, but a quick search suggests that I was wrong.

My little acer has some very vibrant leaves.

In the woods, a whole palette is a treat for the eye.